Roofing Granules with High Solar Reflectance, Roofing Products with High Solar Reflectance, and Processes for Producing Same

ABSTRACT

Solar reflective roofing granules include a binder and inert mineral particles, with solar reflective particles dispersed in the binder. An agglomeration process preferentially disposes the solar reflective particles at a desired depth within or beneath the surface of the granules.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of pending U.S. patent applicationSer. No. 12/601,169, having a 371 date of Mar. 31, 2010, which was anational phase of International Application No. PCT/US2008/064676, filedMay 23, 2008, which claimed the priority of U.S. Provisional PatentApplication Ser. No. 60/939,989 filed May 24, 2007.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present application relates to roofing granules and roofing productsincluding roofing granules, such as roofing shingles.

2. Brief Description of the Prior Art

Asphalt shingles are conventionally used in the United States and Canadaas roofing and siding materials. Roofing granules are typicallydistributed over the upper or outer face of such shingles. The roofinggranules, in general are formed from mineral materials, and serve toprovide the shingle with durability. They protect the asphalt from theeffects of the solar radiation (in particular from the degradativeeffects of ultraviolet rays) and of the environment (wind,precipitation, pollution, and the like), and contribute to betterreflection of incident radiation. The granules moreover are typicallycolored, naturally or artificially by way of the application ofpigments, to meet the aesthetic requirements of the user.

Roofing granules typically comprise crushed and screened mineralmaterials, which are subsequently coated with a binder containing one ormore coloring pigments, such as suitable metal oxides. The binder can bea soluble alkaline silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkaline silicate, resulting in an insoluble colored coating onthe mineral particles. For example, U.S. Pat. No. 1,898,345 to Demingdiscloses coating a granular material with a coating compositionincluding a sodium silicate, a coloring pigment, and a colloidal clay,and heating below the fusing temperature of sodium silicate, andsubsequently treating with a solution, such as a solution of calcium ormagnesium chloride, or aluminum sulphate, that will react with thesodium silicate to form an insoluble compound. Similarly, U.S. Pat. No.2,378,927 to Jewett discloses a coating composition for roofing granulesconsisting of sodium silicate, and clay or another aluminum-bearingcompound such as sodium aluminate, or cryolite or other insolublefluorides such as sodium silicofluoride, and a color pigment. Thecoating is then heat cured at a temperature above the dehydrationtemperature of the coating materials but below the fusion temperature atwhich the combination of materials fuses, thus producing a non-porous,insoluble weather-resistant cement. Roofing granules are typicallyproduced using inert mineral particles with metal-silicate binders andclays as a latent heat reactant at an elevated temperature, for example,such as those described in U.S. Pat. No. 2,981,636. The granules areemployed to provide a protective layer on asphaltic roofing materialssuch as shingles, and to add aesthetic values to a roof.

Pigments for roofing granules have usually been selected to provideshingles having an attractive appearance, with little thought to thethermal stresses encountered on shingled roofs. However, depending onlocation and climate, shingled roofs can experience very challengingenvironmental conditions, which tend to reduce the effective servicelife of such roofs. One significant environmental stress is the elevatedtemperature experienced by roofing shingles under sunny, summerconditions, especially roofing shingles coated with dark colored roofinggranules. Although such roofs can be coated with solar reflective paintor coating material, such as a composition containing a significantamount of titanium dioxide pigment, in order to reduce such thermalstresses, this utilitarian approach will often prove to be aestheticallyundesirable, especially for residential roofs.

Mineral surfaced asphalt shingles, such as those described in ASTM D225or D3462, are generally used in steep-sloped roofs to providewater-shedding function while adding aesthetically pleasing appearanceto the roofs. The asphalt shingles are generally constructed fromasphalt-saturated roofing felts and surfaced by pigmented colorgranules, such as those described in U.S. Pat. No. 4,717,614. Asphaltshingles coated with conventional roofing granules are known to have lowsolar heat reflectance, and hence will absorb solar heat especiallythrough the near infrared range (700 nm-2500 nm) of the solar spectrum.This phenomenon is increased as the granules covering the surface becomedark in color. For example, while white-colored asphalt shingles canhave solar reflectance in the range of 25-35%, dark-colored asphaltshingles can only have solar reflectance of 5-15%. Furthermore, exceptin the white or very light colors, there is typically only a very smallamount of pigment in the conventional granule's color coating thatreflects solar radiation well. As a result, it is common to measuretemperatures as high as 77° C. on the surface of black roofing shingleson a sunny day with 21° C. ambient temperature. Absorption of solar heatmay result in elevated temperatures at the shingle's surroundings, whichcan contribute to the so-called heat-island effects and increase thecooling load to its surroundings. It is therefore advantageous to haveroofing shingles that have high solar reflectivity in order to reducethe solar heat absorption. The surface reflectivity of an asphaltshingle largely depends on the solar reflectance of the granules thatare used to cover the bitumen.

In recent years, the state of California has implemented a building coderequiring the low-sloped roofs to have roof coverings with solarreflectance greater than 70%. To achieve such high level of solarreflectance, it is necessary to coat the roof with a reflective coatingover granulated roofing products, since the granules with currentcoloring technology are not capable of achieving such high levels ofsolar reflectance. However, polymeric coatings applied have only alimited amount of service life and will require re-coat after certainyears of service. Also, the cost of adding such a coating on roofcoverings can be relatively high.

In order to reduce the solar heat absorption, one may use light coloredroofing granules which are inherently more reflective towards the solarradiation. White pigment containing latex coatings have been proposedand evaluated by various manufacturers. However, consumers andhomeowners often prefer darker or earth tone colors for their roof. Inrecent years, there have been commercially available roofing granulesthat feature a reflective base coat (i.e., a white coat) and a partiallycoated top color coat allowing the reflective base coat to be partiallyrevealed to increase solar reflectance. Unfortunately, these granuleshave a “washed-out” color appearance due to the partially revealed whitebase coat.

Other manufactures have also proposed the use of exterior-grade coatingsthat were colored by infrared-reflective pigments for deep-tone colorsand sprayed onto the roof in the field. U.S. Patent ApplicationPublication No. 2003/0068469 A1 discloses an asphalt-based roofingmaterial comprising mat saturated with an asphalt coating and a topcoating having a top surface layer that has a solar reflectance of atleast 70%. U.S. Patent Application Publication No. 2003/0152747 A1discloses the use of granules with solar reflectance greater than 55%and hardness greater than 4 on the Moh's scale to enhance the solarreflectivity of asphalt based roofing products. However, there is nocontrol of color blends and the novel granules are typically availableonly in white or buff colors. U.S. Patent Application Publication No.2005/0074580 A1 discloses a non-white construction surface comprising afirst reflective coating and a second reflective coating with totaldirect solar reflectance of at least 20%.

Also, there have been attempts in using special near-infrared reflectivepigments in earth-tone colors to color roofing granules for increasedsolar reflectance. However, the addition of kaolin clays, which are usedto make the metal-silicate binder durable through heat curing,inevitably reduce the color strength or the color intensity of thepigment.

Colored roofing granules can also be prepared using a metal silicatebinder without adding clay and curing the binder at temperatures greaterthan glass sintering temperature, or through a “pickling” process byapplying acid. However, these alternatives require either very hightemperatures, or the use of corrosive chemicals, and in many cases couldresult in loss of color due to pigment degradation by the acid.

In the alternative, a non-silicate binder, such as a synthetic polymericbinder, can be used to coat the inert mineral materials in order toproduce roofing granules with dark colors and high solar reflectance.However, the long-term durability and cost for polymeric coatings arenot as advantageous as the silicate binders.

Another approach is provided by solar control films that contain eitherthin layer of metal/metal oxides or dielectric layers through vacuumdeposition, and which have been commercially available for use inarchitectural glasses.

There is a continuing need for roofing materials, and especially asphaltshingles, that have improved resistance to thermal stresses whileproviding an attractive appearance.

SUMMARY OF THE INVENTION

The present invention provides roofing granules, which have high solarreflectance, such as at least 70 percent, as well as roofing productssuch as shingles provided with such solar reflective roofing granules.The present invention also provides a process for preparing solarreflective roofing granules. In one presently preferred embodiment, theprocess of the present invention comprises providing a binder, inertmineral particles, and solar reflective particles, dispersing the inertmineral particles and the solar reflective particles in the binder toform a mixture, forming the mixture into uncured granules; and curingthe binder to form cured roofing granules. Preferably, the process ofthe present invention includes selecting the solar reflective particlesto provide granules having greater than about 60 percent, and morepreferably greater than about 70 percent solar reflectance.

In another presently preferred embodiment, the present inventionprovides a process for preparing solar reflective roofing granulescomprising providing a binder and inert mineral particles to form amixture, forming the mixture into uncured granule bodies having anexterior surface, adhering solar reflective particles to the exteriorsurface of the uncured granule bodies, and curing the binder. In oneaspect of this embodiment of the process of the present invention, thesolar reflective particles are mechanically adhered to the exteriorsurface of the uncured granule bodies. In another aspect of thisembodiment of the process of the present invention, the process furthercomprises mixing the solar reflective particles with a fluid carrier toform a paste or coating and adhering the solar reflective particles tothe exterior surface of the granule bodies by applying the paste to theexterior surface of the granule bodies.

Preferably, the process further comprises sizing the uncured granules byscreening. In one presently preferred embodiment of the process of thepresent invention, the uncured granules are heated to cure the binder.In one aspect, the present process further comprises surface treatingthe cured roofing granules. In one presently preferred embodiment of theprocess of the present invention, the inert mineral particles compriseuncalcined kaolin, the binder comprises metal silicate, and the binderis cured by heating the uncured granules at from about 500 degrees C. to800 degrees C.

The present invention also provides solar reflective roofing granulescomprising a binder, inert mineral particles, and solar reflectiveparticles, with the inert mineral particles and the solar reflectiveparticles being dispersed in the binder. Preferably, the solarreflective particles are selected from the group consisting of titaniumdioxides, metal pigments, titanates, and metal reflective pigments.Preferably, the inert mineral particles have an average particle sizefrom about 0.1 micrometers to 40 micrometers, and more preferably fromabout 0.25 micrometers to 20 micrometers. Preferably, the solarreflective roofing granules themselves have an average particle sizefrom about 0.1 mm to 3 mm, and more preferably from about 0.5 mm to 1.5mm. Preferably, the binder is selected from the group consisting ofsilicate, silica, phosphate, titanate, zirconate, and aluminate binders,and mixtures thereof. In one aspect, the binder preferably furthercomprises an inorganic material selected from the group consisting ofaluminosilicate and kaolin clay.

In another aspect, the present invention also provides a process forpreparing solar reflective roofing granules, in which the processcomprises providing ceramic particles; forming the ceramic particlesinto uncured granule bodies having an exterior surface; adhering solarreflective particles to the exterior surface of the uncured granulebodies; and sintering the uncured granule bodies to form solarreflective roofing granules. Preferably, the solar reflective particlesare mechanically adhered to the exterior surface of the uncured granulebodies. In this aspect, the present process further preferably comprisesproviding a sintering binder and mixing the sintering binder with theceramic particles to form a mixture and subsequently forming the mixtureincluding the ceramic particles into uncured granule bodies. In thisaspect, the present invention also provides solar reflective roofinggranules having an exterior surface, the roofing granules comprisingsintered ceramic particles; and solar reflective particles; wherein atleast some of the solar reflective particle are proximate the exteriorsurface of the solar reflective particles. Preferably, the solarreflective particles are selected from the group consisting of titaniumdioxides, metal pigments, titanates, and metal reflective pigments.

The present invention also provides roofing products, such as bituminousroofing shingles, including solar reflective roofing granules accordingto the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional elevational representation of a roofinggranule according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional elevational representation of a roofinggranule according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional elevational representation of a roofinggranule according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional elevational representation of a roofinggranule according to a fourth embodiment of the present invention.

FIG. 4a is a partial fragmentary schematic sectional elevationalrepresentation of the roofing granule of FIG. 4.

FIG. 5 is a partial fragmentary schematic sectional elevationalrepresentation according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION

As used in the present specification and claims, “solar reflective,” and“solar heat-reflective” refer to reflectance in the near infrared range(700 to 2500 nm) of the electromagnetic spectrum, and “high solarreflectance” means having an average reflectance of at least about 70percent over the near infrared range (700 to 2500 nm) of theelectromagnetic spectrum.

As used in the present specification and claims, “solar reflectiveparticle” means a particulate material having a solar reflectance of atleast 60 percent, and preferably at least about 70 percent.

As used in the present specification and claims, “solar reflectivefunctional pigment” denotes a pigment selected from the group consistingof light-interference platelet pigments including mica,light-interference platelet pigments including titanium dioxide,mirrorized silica pigments based upon metal-doped silica, metal flakepigments, metal oxide coated flake pigments, and alumina. As used in thepresent specification and claims, “granule coloring pigment” denotes aconventional metal oxide-type pigment employed to color roofinggranules.

Preferably, the present invention provides highly reflective, solid,durable, and crush-resistance granules suitable for roofing applicationswith the sizes ranging from −10 to +40 U.S. mesh.

Preferably, the solar reflective roofing granules according to thepresent invention have a solar reflectance of at least about 60 percent,and more preferably at least about 70 percent.

Roofing granules according to the present invention can be made bysynthetically forming a “green” or uncured granule body, adhering highlysolar reflective particles to the uncured granule body, and curing theuncured granule body.

The mineral particles employed in the process of the present inventionare preferably chemically inert materials. The mineral particlespreferably have an average particle size of from about 0.1 micrometersto about 40 micrometers, and more preferably from about 0.25 micrometersto about 20 micrometers. Stone dust can be employed as the source of themineral particles in the process of the present invention. Stone dust isa natural aggregate produced as a by-product of quarrying, stonecrushing, machining operations, and similar operations. In particular,dust from talc, slag, limestone, granite, marble, syenite, diabase,greystone, quartz, slate, trap rock, basalt, greenstone, andesite,porphyry, rhyolite, greystone, and marine shells can be used, as well asmanufactured or recycled manufactured materials such as ceramic grog,proppants, crushed bricks, concrete, porcelain, fire clay, and the like.Ceramic materials, such as silicon carbide and aluminum oxide ofsuitable dimensions can also be used. Preferably, the mineral particlesare manufactured from crushing naturally occurring rocks with low freesilica into suitable sizes for their UV opacity and protection toasphalt when the roofing granules according to the present invention areemployed to protect bituminous roofing materials such as asphaltshingles. Such silica-deficient rocks are generally dark in color andhave low solar reflectance in the range around 8 to 15 percent.Conventionally, it is necessary to coat granules prepared from thesenaturally-derived rocks with heavy coatings or multiple coats in orderto significantly increase the solar reflectance. Even so, the highestachievable solar reflectance is only limited to about 60%. Although onemay reduce the particle sizes to further increase the solar reflectance,the surface coverage and the exposure of asphalt can be affected.

Advantageously, the process of the present invention can produce highlyreflective granules that do not require additional coatings to achievehigh solar reflectance, such as 70 percent solar reflectance, whileproviding particle size distributions similar to conventional #11-graderoofing granules.

Thus, the present invention provides a process for preparing solarreflective roofing granules. In one aspect, the process of the presentinvention comprises providing a binder, inert mineral particles, andsolar reflective particles; dispersing the inert mineral particles andthe solar reflective particles in the binder to form a mixture; formingthe mixture into uncured or “green” granules or granule bodies; andcuring the binder.

The granules can be formed by the methods disclosed in United StatesPatent Publication 2004/0258835 A1, incorporated herein by reference.

The “green” or uncured granules can be formed by using relativelylow-cost raw materials, such as clay and/or granule dust from the wastestream of granule crushing, and adding water and/or a suitable binderfollowed by a suitable granulation or agglomeration process to form theuncured granules.

The solar reflective particles can be directly incorporated into theuncured granules by blending with other starting raw materials, or thesolar reflective particles can be added during a later stage of thegranulation/agglomeration step. In the alternative, the solar reflectiveparticles can be added to the surface of the formed uncured granuleseither by blending the solar reflective particles in the form of a drypowder with the still moist, uncured granules, or coating the uncuredgranules in a form of a paste or coating.

In one aspect of the process of the present invention, “green” oruncured granules can be formed from a mixture of mineral particles,solar reflective particles and binder, ranging from about 95% by weightbinder to less than about 10% by weight binder, and the uncured solarreflective roofing granules preferably are formed from a mixture thatincludes from about 10% to 40% by weight binder.

The binder can be a binder selected from the group consisting ofsilicate, silica, phosphate, titanate, zirconate, and aluminate binders,and mixtures thereof. The binder can further comprise an inorganicmaterial selected from the group consisting of aluminosilicate andkaolin clay. In one aspect of the present invention, the binder is asoluble alkali metal silicate, such as aqueous sodium silicate oraqueous potassium silicate. The soluble alkali metal silicate issubsequently insolubilized by heat or by chemical reaction, such as byreaction between an acidic material and the alkali metal silicate,resulting in cured solar reflective granules. The binder may alsoinclude additives for long term outdoor durability and functionality.

When an alkali metal-silicate binder such as sodium silicate is employedin the preparation of solar reflective roofing granules, the binder caninclude a heat-reactive aluminosilicate material, such as clay, forexample, kaolin clay. Alternatively, it is possible to insolubilize themetal silicate binder chemically by reaction with an acidic material,for example, ammonium chloride, aluminum chloride, hydrochloric acid,calcium chloride, aluminum sulfate, and magnesium chloride, such asdisclosed in U.S. Pat. Nos. 2,591,149, 2,614,051, 2,898,232 and2,981,636, or other acidic material such as aluminum fluoride. Thebinder can also be a controlled release sparingly water soluble glasssuch as a phosphorous pentoxide glass modified with calcium fluoride,such as disclosed in U.S. Pat. No. 6,143,318. The most commonly usedbinder for conventional granule coating is a mixture of an alkali metalsilicate and an alumino-silicate clay material.

The mixture of mineral particles, solar reflective particles and bindercan be formed into uncured solar reflective roofing granules, using aforming process such as press, molding, cast molding, injection molding,extrusion, spray granulation, gel casting, pelletizing, compaction, oragglomeration. Preferably, the resulting uncured solar reflectiveroofing granules have sizes between about 50 micrometer and 5 mm, morepreferably between about 0.1 mm and 3 mm, and still more preferablybetween about 0.5 mm and 1.5 mm. The uncured solar reflective roofinggranules can be formed using a conventional extrusion apparatus. Forexample, aqueous sodium silicate, kaolin clay, mineral particles, andsolar reflective particles and water (to adjust mixability) can becharged to a hopper and mixed by a suitable impeller before being fed toan extrusion screw provided in the barrel of the extrusion apparatus,such as disclosed, for example, in United States Patent Publication2004/0258835 A1. Alternatively, the ingredients can be charged to theextruder continuously by gravimetric feeds. The screw forces the mixturethrough a plurality of apertures having a predetermined dimensionsuitable for sizing roofing granules. As the mixture is extruded, theextrudate is chopped by suitable rotating knives into a plurality ofuncured solar reflective roofing granules, which are subsequently firedat an elevated temperature to sinter or densify the binder.

When the formed granules are fired, such as in a rotary kiln, at anelevated temperature, such as at least 800 degrees C., and preferably at1,000 to 1,200 degrees C., and the binder densifies to form solid,durable, and crush-resistance granules.

Examples of clays that can be employed in the process of the presentinvention include kaolin, other aluminosilicate clays, Dover clay,bentonite clay, etc.

Suitable solar reflective particles include titanium dioxides such asrutile titanium dioxide and anatase titanium dioxide, metal pigments,titanates, and mirrorized silica pigments.

Examples of mirrorized silica pigments that can be employed in theprocess of the present invention include pigments such as Chrom Brite™CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge,N.Y. 11788.

Examples of rutile titanium dioxide and anatase titanium dioxide thatcan be employed in the solar reflective roofing granules of the presentinvention include R-101 which are available from Du Pont de Nemours,P.O. Box 8070, Wilmington, Del. 19880.

Examples of metal pigments that can be employed in the solar reflectiveroofing granule of the present invention include aluminum flake pigment,copper flake pigments, copper alloy flake pigments, and the like. Metalpigments are available, for example, from ECKART America Corporation,Painesville, Ohio 44077. Suitable aluminum flake pigments includewater-dispersible lamellar aluminum powders such as Eckart RO-100,RO-200, RO-300, RO-400, RO-500 and RO-600, non-leafing silica coatedaluminum flake powders such as Eckart STANDART PCR-212, PCR 214, PCR501, PCR 801, and PCR 901, and STANDART Resist 211, STANDART Resist 212,STANDART Resist 214, STANDART Resist 501 and STANDART Resist 80;silica-coated oxidation-resistant gold bronze pigments based on copperor copper-zinc alloys such as Eckart DOROLAN 08/0 Pale Gold, DOROLAN08/0 Rich Gold and DOROLAN 10/0 Copper.

Examples of titanates that can be employed in the solar reflectiveroofing granules of the present invention include titanate pigments suchas colored rutile, priderite, and pseudobrookite structured pigments,including titanate pigments comprising a solid solution of a dopantphase in a rutile lattice such as nickel titanium yellow, chromiumtitanium buff, and manganese titanium brown pigments, priderite pigmentssuch as barium nickel titanium pigment; and pseudobrookite pigments suchas iron titanium brown, and iron aluminum brown. The preparation andproperties of titanate pigments are discussed in Hugh M. Smith, HighPerformance Pigments, Wiley-VCH, pp. 53-74 (2002).

Examples of near IR-reflective pigments available from the ShepherdColor Company, Cincinnati, Ohio, include Arctic Black 10C909 (chromiumgreen-black), Black 411 (chromium iron oxide), Brown 12 (zinc ironchromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chromeantimony titanium).

Aluminum oxide, preferably in powdered form, can be used assolar-reflective additive in the color coating formulation to improvethe solar reflectance of colored roofing granules without affecting thecolor. The aluminum oxide should have particle size less than #40 mesh(425 micrometers), preferably between 0.1 micrometers and 5 micrometers.More preferably, the particle size is between 0.3 micrometers and 2micrometers. The alumina should have a percentage of aluminum oxidegreater than 90 percent, more preferably greater than 95 percent.Preferably the alumina is incorporated into the granule so that it isconcentrated near and/or at the outer surface of the granule.

In addition, granule coloring pigments such as iron oxide, whitepigments such as lithopone, zinc sulfide, zinc oxide, and lead oxide,void pigments such as spherical styrene/acrylic beads (Ropaque® beads,Rohm and Haas Company), and/or hollow glass beads having pigmentary sizefor increased light scattering, can also be mixed with the solarreflective particles and mineral particles and binder to form theuncured granules, or with the solar reflective particles to be adheredto the exterior surface of the uncured granules. In the case where anorganic polymeric void pigment is employed, a lower temperature cycle isdesirable to avoid alteration of or damage to such pigment.

A colored, infrared-reflective pigment can also be employed in preparingthe solar reflective roofing granules of the present invention.Preferably, the colored, infrared-reflective pigment comprises a solidsolution including iron oxide, such as disclosed in U.S. Pat. No.6,174,360, incorporated herein by reference. The coloredinfrared-reflective pigment can also comprise a near infrared-reflectingcomposite pigment such as disclosed in U.S. Pat. No. 6,521,038,incorporated herein by reference. Composite pigments are composed of anear-infrared non-absorbing colorant of a chromatic or black color and awhite pigment coated with the near-infrared non-absorbing colorant.Near-infrared non-absorbing colorants that can be used in the presentinvention are organic pigments such as organic pigments including azo,anthraquinone, phthalocyanine, perinone/perylene, indigo/thioindigo,dioxazine, quinacridone, isoindolinone, isoindoline,diketopyrrolopyrrole, azomethine, and azomethine-azo functional groups.Preferred black organic pigments include organic pigments having azo,azomethine, and perylene functional groups. When organic colorants areemployed, a low temperature cure process is preferred to avoid thermaldegradation of the organic colorants.

The solar-reflective roofing granules of the present invention caninclude conventional coatings pigments. Examples of coatings pigmentsthat can be used include those provided by the Color Division of FerroCorporation, 4150 East 56th St., Cleveland, Ohio 44101, and producedusing high temperature calcinations, including PC-9415 Yellow, PC-9416Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow, V-9186Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248 Blue,PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600 CamouflageGreen, V12560 IR Green, V-778 IR Black, and V-799 Black.

The solar reflective roofing granules of the present invention can alsoinclude light-interference platelet pigments. Light-interferenceplatelet pigments are known to give rise to various optical effects whenincorporated in coatings, including opalescence or “pearlescence.”

Examples of light-interference platelet pigments that can be employed inthe process of the present invention include pigments available fromWenzhou Pearlescent Pigments Co., Ltd., No. 9 Small East District,Wenzhou Economical and Technical Development Zone, Peoples Republic ofChina, such as Taizhu TZ5013 (mica, rutile titanium dioxide and ironoxide, golden color), TZ5012 (mica, rutile titanium dioxide and ironoxide, golden color), TZ4013 (mica and iron oxide, wine red color),TZ4012 (mica and iron oxide, red brown color), TZ4011 (mica and ironoxide, bronze color), TZ2015 (mica and rutile titanium dioxide,interference green color), TZ2014 (mica and rutile titanium dioxide,interference blue color), TZ2013 (mica and rutile titanium dioxide,interference violet color), TZ2012 (mica and rutile titanium dioxide,interference red color), TZ2011 (mica and rutile titanium dioxide,interference golden color), TZ1222 (mica and rutile titanium dioxide,silver white color), TZ1004 (mica and anatase titanium dioxide, silverwhite color), TZ4001/600 (mica and iron oxide, bronze appearance),TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance),TZ1001/80 (mica and titanium dioxide, off-white appearance), TZ2001/600(mica, titanium dioxide, tin oxide, off-white/gold appearance),TZ2004/600 (mica, titanium dioxide, tin oxide, off-white/blueappearance), TZ2005/600 (mica, titanium dioxide, tin oxide,off-white/green appearance), and TZ4002/600 (mica and iron oxide, bronzeappearance).

Examples of light-interference platelet pigments that can be employed inthe process of the present invention also include pigments availablefrom Merck KGaA, Darmstadt, Germany, such as Iriodin® pearlescentpigment based on mica covered with a thin layer of titanium dioxideand/or iron oxide; Xirallic™ high chroma crystal effect pigment basedupon Al2O3 platelets coated with metal oxides, including Xirallic T60-10 WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold, andXirallic F 60-50 WNT fireside copper; ColorStream™ multi color effectpigments based on SiO2 platelets coated with metal oxides, includingColorStream F 20-00 WNT autumn mystery and ColorStream F 20-07 WNT violafantasy; and ultra interference pigments based on titanium dioxide andmica.

The amount of solar reflective particles added is preferably such thatthe resultant solar reflective roofing granules have a solar reflectanceof at least about 60 percent, and preferably at least about 70 percent,while not unduly adversely affecting granulation.

In one presently preferred embodiment uncalcined kaolin can be employedas the source of mineral particles and metal-silicates can be employedas binder to form uncured granules. In this case, it is preferred thatthe kaolin can be formed into granule body by a suitable granulation oragglomeration process and permitted to dry to an uncured green bodyeither by simple rotary dryer, in a fluidized bed drier, or by drying inan oven in a suitable tray or on a continuous belt. The reflectivepigments can then be incorporated into sodium silicate and the resultantmixture can then be soaked into the green body of kaolin clay due to itshigh porosity and capillary forces. Advantageously, the resultantuncured granules can be heat cured at a temperature ranging from about500 to 800 degrees C. to react the kaolin and the sodium silicate, whichcan be handled by simple kiln or dryer to further reduce manufacturingcost, to form durable, hard granules suitable for roofing applications.

The resultant granules can also be surface treated with siliconates orsuitable oils to enhance its adhesion to asphalt and also to reducetheir staining potentials.

Other methods of forming a granular body and incorporating solarreflective particles during the formation of the said body will becomeapparent to those who are skilled in the art.

In yet another aspect of the present invention, the binder comprises achemically bonded cement, preferably, a chemically bonded phosphatecement. It is preferred in this aspect that the binder comprise achemically bonded phosphate cement prepared from a cementitious exteriorcoating composition including at least one metal oxide or a metalhydroxide slightly soluble in an acidic aqueous solution to providemetal cations and a source of phosphate anions. Preferably, the relativequantities of the at least one metal oxide or metal hydroxide and atleast one source of phosphate anion are selected to provide a curedcoating having a neutral pH, the coating composition being cured by theacid-base reaction of the at least one metal oxide or hydroxide and thesource of phosphate anions. Preferably, in this aspect the bindercomprises at least one metal oxide or metal hydroxide as a source ofmetal cations and at least one phosphate. Preferably, at least one metaloxide or metal hydroxide comprises at least one clay. Preferably, thebinder further includes colloidal silica.

Preferably, the at least one metal oxide or metal hydroxide is selectedfrom the group consisting of alkali earth metal oxides, alkaline earthhydroxides, aluminum oxide, oxides of first row transition metals,hydroxides of first row transition metals, oxides of second rowtransition metals, and hydroxides of second row transition metals. Morepreferably, the at least one metal oxide or metal hydroxide is selectedfrom the group consisting of magnesium oxide, calcium oxide, iron oxide,copper oxide, zinc oxide, aluminum oxide, cobalt oxide, zirconium oxideand molybdenum oxide. Preferably, the at least one metal oxide or metalhydroxide is sparingly soluble in an acidic aqueous solution. Inaddition, it is preferred that the at least one metal oxide or metalhydroxide comprise from about 10 to 30% by weight of the binder.

Preferably, the at least one phosphate is selected from the groupconsisting of phosphoric acid and acid phosphate salts. More preferably,the at least phosphate is selected from the group consisting ofphosphoric acid, and acid salts of phosphorous oxo anions, andespecially salts including at least one cation selected from the groupconsisting of ammonium, calcium, sodium, potassium, and aluminumcations. In particular, it is preferred that the at least one phosphatebe selected from the group consisting of phosphoric acid, ammoniumhydrogen phosphate, ammonium dihydrogen phosphate, potassium hydrogenphosphate, potassium dihydrogen phosphate, potassium phosphate, calciumhydrogen phosphate, calcium dihydrogen phosphate, magnesium hydrogenphosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate,aluminum hydrogen phosphate, aluminum dihydrogen phosphate, and mixturesthereof. Commercial grades of calcium phosphate salts, such “NSP”(normal super phosphate) and “TSP” (triple super phosphate) can also beused. Potassium dihydrogen phosphate (“monopotassium phosphate”),aluminum hydrophosphate (AlH₃(PO₄).2H₂O), monoaluminum phosphate(Al(H₂PO₄)₃) and magnesium dihydrogen phosphate are especiallypreferred. Preferably, the at least one phosphate comprises from about10 to 60% by weight of the binder.

In this aspect of solar reflective roofing granules according to thepresent invention, the cure of the binder depends on the composition ofthe chemically bonded cement. A broad range of cure conditions, rangingfrom rapid room temperature curing to low energy cures at moderatelyelevated temperatures to high energy cures at more elevated temperaturescan be attained by varying the metal oxide or hydroxide and thephosphate. Optionally, the reactivity of the metal oxide or hydroxidecan be reduced by calcining the metal oxide or metal hydroxide prior topreparing the binder. In addition, the pot life of the binder can beextended by the optional addition of a retardant such as boric acid.

In another aspect, the solar reflective roofing granules according tothe present invention can include an inert mineral core material,covered with a layer of mineral particles, solar reflective particles,and binder.

The inert mineral core material can be a suitably sized mineral particlesuch as described above, or in the alternative, the mineral corematerial can be a solid or hollow glass spheres. Solid and hollow glassspheres are available, for example, from Potters Industries Inc., P. O.Box 840, Valley Forge, Pa. 19482-0840, such as SPHERIGLASS® solid “A”glass spheres product grade 1922 having a mean size of 0.203 mm, productcode 602578 having a mean size of 0.59 mm, BALLOTTINI impact beadsproduct grade A with a size range of 600 to 850 micrometers (U.S. sievesize 20-30), and QCEL hollow spheres, product code 300 with a meanparticle size of 0.090 mm. Glass spheres can be coated or treated with asuitable coupling agent if desired for better adhesion to the binder ofthe coating composition.

In another aspect of the present invention, solar reflective roofinggranules are produced by an accretion process such as disclosed in U.S.Pat. No. 7,067,445, incorporated herein in its entirety by reference.The starting materials employed are mineral particles and binder, andoptionally solar reflective particles. The starting materials arepreferably ground, if necessary, by ball milling or another attritionprocess, to form particles having a mean particle size of about 20microns or less, more preferably, about 15 microns or less, and mostpreferably about 10 microns or less, expressed in terms of particlediameter (or average diameter for non-spherical particles). The groundstarting materials are combined with a liquid, such as water, and mixedin an intensive mixer, such as an Eirich mixer (Eirich Machines Inc.,Gurnee, Ill. 60031) having a rotatable confinement vessel having arotatable table, or pan, and a rotatable impacting impeller. In anintensive mixer the rotatable table and impeller rotate in oppositedirections. Sufficient water or other liquid is added to causeessentially spherical pellets of the starting material mixture to beformed (about 15 to 40 weight percent water based on the startingmaterials). After such pellets have formed, a second mixture is added,and the mixture is further operated to cause accretion of the addedmaterial to the pellets being formed. The second mixture includes solarreflective particles and binder, and optionally mineral particles andcolorant material particles. The second mixture preferable comprises upto 25 percent, and more preferably, from about 5 to 15 percent byweight, of the starting materials. The pellet so formed are then driedto a moisture content of less than about 10 weight percent, for example,in a drier at a temperature between about 100 degree C. and 300 degreesC. to form “green” roofing granules. The “green” roofing granules soformed are subsequently cured. Depending on the nature of the binder,the “green” granules can be cured by heating at an elevated temperatureto cure the binder. For example, when the binder comprises aqueoussodium silicate and kaolin clay, the “green” granules can be cured byheating at a temperature between about 400 degrees C. and 800 degrees C.to solidify the binder.

In another aspect of the present invention, solar reflective roofinggranules are produced by an accretion process similar to that disclosedin U.S. Pat. No. 7,067,445. In this aspect of the present invention, thestarting materials employed are ceramic particles and a sinter binder,and optionally solar reflective particles.

Suitable ceramic particles include oxides, such as aluminum oxides, suchas alumina, silicon oxides, such as silica, and mixtures thereof.Preferably, the ceramic particles comprise silica and alumina, andcomprise at least 80 percent by weight of the starting materials,expressed in terms of the calcined (essentially anhydrous) weight, andmore preferably, at least about 90 percent of the calcined weight.

“Calcined” as used herein refers to a heating process to which amaterial has been subjected to release water and other volatiles fromthe material, such as organic materials and chemically bound water suchwater of hydration. Ore materials that have been fully calcined exhibitvery low loss on ignition (“LOI”) and moisture content, for example,about 1 to 2 percent by weight or less. Uncalcined ore materials such asbauxites and clays can contain from about 10 to about 40 percentvolatiles. “Partially calcined” material typically exhibit totalvolatiles (LOI and moisture content) of about 5 to 8 percent. Typicalcalcination temperatures are usually less than 1000 degrees C.

The ceramic particles can be clays (predominantly hydrated alumina) suchas kaolin, diaspore clay, burley clay, flint clay, bauxitic clays,nature or synthetic bauxites, mixtures thereof and the like. The ceramicparticles can be calcined or partially calcined. The ceramic particlesare preferably formed from oxides, aluminates, and silicates, such asmagnesium silicates, and preferably comprise up to 50 percent by weight,more preferably at least 90 percent by weight, and most preferably atleast 90 percent by weight of the starting materials.

The starting materials can also include various sintering aids, such asbentonite clay, iron oxide, boron, boron carbide, aluminum diboride,boron nitride, boron phosphide, other boron compounds, or fluxes such assodium carbonate, lithium carbonate, titania, calcium carbonate, andsodium silicate, which materials can be added in amounts up to about 10percent by weight to aid in sintering.

In addition, a sintering binder, such as wax, a starch, or resin, suchas gelatinized cornstarch, polyvinyl alcohol, or mixture thereof, can beadded to the initial mixture to aid in pelletizing the mixture andincrease the green strength of the pellets prior to sintering. Thesintering binder can be added in an amount of about 0 to 6 percent byweight of the starting materials.

The starting materials are preferably ground, if necessary, by ballmilling or another attrition process, to form particles having a meanparticle size of about 20 microns or less, more preferably, about 15microns or less, and most preferably about 10 microns or less, expressedin terms of particle diameter (or average diameter for non-sphericalparticles). The ground starting materials are combined with a liquid,such as water, and mixed in an intensive mixer. Sufficient water orother liquid is added to cause essentially spherical pellets of thestarting material mixture to be formed (about 15 to 40 weight percentwater based on the starting materials). After such pellets have formed,a second mixture is added, and the mixture is further operated to causeaccretion of the added material to the pellets being formed. The secondmixture includes solar reflective particles and sintering binder, andoptionally ceramic particles, sintering aid, and colorant materialparticles. The second mixture preferable comprises up to 25 percent, andmore preferably, from about 5 to 15 percent by weight, of the startingmaterials. The pellet so formed are then dried to a moisture content ofless than about 10 weight percent, for example, in a drier at atemperature between about 100 degree C. and 300 degrees C. to form“green” roofing granules.

The “green” roofing granules so formed are subsequently sintered in afurnace at a sintering temperature until a specific gravity of fromabout 2.1 to 4.1 grams per cubic centimeter is obtained, depending onthe composition of the starting materials, and the desired specificgravity of the roofing granules. Sintering generally causes a reductionof up to about 20 percent in pellet size as well as an increase inspecific gravity. Suitable sintering temperatures are generally about1150 degrees C. and above, more preferably at about 1300 degrees C.,still more preferably about 1500 degrees C., although sinteringtemperatures can be as high as 1600 degrees C.

In another aspect, roofing granule core particles are prepared by asintering process as described above, and are subsequently treated toprovide a surface layer with a desired functionality, such as solarreflectivity, biocidal activity, or other functionality. The surfacecoating can include solar reflective particles and a binder curable attemperatures below the sintering range. In this case, the solarreflective particles can optionally be omitted from the core particles.Thus, in this aspect the surface coating can be formed from a coatingcomposition including a binder selected from the group consisting ofsilicate, silica, phosphate, titanate, zirconate, and aluminate binders,and mixtures thereof, and the binder can further comprise an inorganicmaterial selected from the group consisting of aluminosilicate andkaolin clay.

Referring now to the drawings, in which like reference numerals refer tolike elements in each of the several views, there are shownschematically in FIGS. 1, 2, and 3 examples of solar reflective roofinggranules according to the present invention.

FIG. 1 is a schematic cross-sectional representation of a firstembodiment of solar reflective roofing granule 10 according to thepresent invention. The solar reflective roofing granule 10 comprises aplurality of inert mineral particles 12 and solar reflective particles14 dispersed in a binder 16. The solar reflective roofing granule 10 hasan exterior surface 18. Solar reflectance is provided to the solarreflective roofing granule 10 by virtue of the solar reflectiveparticles 14 provided at or proximate the exterior surface 18 of thesolar reflective roofing granule 10. The solar reflective roofinggranule 10 can be formed by extrusion, agglomeration, roll compaction orother forming techniques. While the solar reflective roofing granule 10is shown schematically as a sphere in FIG. 1, solar reflective roofinggranules according to the present invention can assume any regular orirregular shape. After formation, depending on binder chemistry and thenature of the colorant, the solar reflective roofing granule 10 can befired at 250 degrees C. or higher (or less, in the case of organiccolorants), preferably from 500 degrees C. to 800 degrees C., toinsolubilize the binder 16. The particle size of the solar reflectiveroofing granule 10 preferably ranges from about 0.1 mm to 3 mm, and morepreferably from about 0.5 mm to 1.5 mm. The inert mineral particles 12are minute particulates or dust, such as for example, particulates ofrhyolite, syenite, bauxite and other rock sources formed as a byproductfrom quarry, crushing and similar operations. The inert mineralparticles 12 preferably have a particle size ranging from about 0.1micrometer to 40 micrometers, and more preferably from about 0.25micrometer to 20 micrometers. The binder 16 is preferably selected fromthe group consisting of silicate, silica, phosphate, titanate, zirconateand aluminate binders, and mixtures thereof. The binder content of thesolar reflective roofing granule 10 preferably ranges from 10% to 90% byweight. In addition, aluminosilicate, kaolin clay and other inorganicmaterials can be added to the binder 16 to improve the mechanical,chemical, or physical properties of the solar reflective roofing granule10.

FIG. 2 is a schematic cross-sectional representation of a secondembodiment of solar reflective roofing granule 20 according to thepresent invention. The solar reflective roofing granule 20 comprises aplurality of inert mineral particles 22 dispersed in a binder 26, andsolar reflective particles 24 adhered to the exterior surface 28 of thesolar reflective roofing granule 20. The solar reflective granules 20 ofthis second embodiment can be prepared by mixing the inert mineralparticles 22 with the binder 26 and forming uncured granule bodies (notshown) from the mixture by granulation, agglomeration or anothertechnique. The mixture is preferably prepared so that the binder remainssomewhat tacky or adhesive after the uncured granule bodies have beenformed. The uncured granule bodies are then dusted with the solarreflective particles 24 so that the solar reflective particlesmechanically adhere to the exterior surface of the uncured granulebodies to form uncured roofing granules (not shown). The uncured roofinggranules are then subjected to elevated temperature to cure the binderto form the solar reflective roofing granules 20.

FIG. 3 is a schematic cross-sectional representation of a thirdembodiment of a solar reflective roofing granule 30 according to thepresent invention. The solar reflective roofing granule 30 comprises aplurality of inert mineral particles 32 dispersed in a binder 36 to forman inert composite mineral body or granule body 35 having an exteriorsurface 38, covered with a plurality of solar reflective particles 34dispersed in an exterior binder 40. Solar reflective activity isprovided to the solar reflective roofing granule 30 by virtue of thesolar reflective particles 34 provided at or proximate the exteriorsurface 39 of the solar reflective roofing granule 30. The solarreflective roofing granules 30 of this third embodiment can be preparedby mixing the inert mineral particles 32 with the binder 36 and forminguncured granule bodies (not shown) from the mixture by granulation oranother technique. The uncured granule bodies are then covered with aslurry of the solar reflective particles 34 dispersed in another bindermaterial 40 so that the slurry of solar reflective particles 34 adheresto the exterior surface of the uncured granule bodies to form uncuredroofing granules (not shown). The uncured roofing granules are thensubjected to elevated temperature to cure the binder to form the solarreflective roofing granules 30. The binder 40 employed to form theslurry of solar reflective particles 34 can be the same as that employedto form the uncured granule bodies, or a different binder can beemployed.

FIG. 4 is a schematic cross-sectional representation of a fourthembodiment of a solar reflective roofing granule 40 according to thepresent invention. The solar reflective roofing granule 40 comprises aplurality of inert mineral particles 42 and dispersed in a binder 46 aswell as an exterior layer 50 of solar reflective particles 44 dispersedin binder 46 proximate the surface of the roofing granule 40, and formedby a particle accretion process in an intensive mixer. The exteriorlayer 50 can have a thickness of from about 20 micrometers to 200micrometers. The exterior layer 50 can also include particulatecolorants 49 or dyes, better seen in the partial fragmentary view ofFIG. 4 a.

FIG. 5 is a fragmentary schematic cross-sectional representation of afifth embodiment of a solar reflective roofing granule 60 according tothe present invention. The solar reflective roofing granule 60 comprisesa plurality of sintered ceramic particles 62 and an exterior layer 70 ofsolar reflective particles 64 sintered to the ceramic particles 62proximate to the surface the roofing granule 60, and formed by aparticle accretion process in an intensive mixer to form green pellets,followed by sintering at an elevated temperature. The exterior layer 70can have a thickness of from about 20 micrometers to 200 micrometers.The exterior layer 90 can also include particulate colorants 69,sintered to the ceramic particles 62 and/or solar reflective particles64.

The solar reflective roofing granules of the present invention can beemployed in the manufacture of roofing products, such as asphaltshingles and bituminous membranes, using conventional roofing productionprocesses. Typically, bituminous roofing products are sheet goods thatinclude a non-woven base or scrim formed of a fibrous material, such asa glass fiber scrim. The base is coated with one or more layers of abituminous material such as asphalt to provide water and weatherresistance to the roofing product. One side of the roofing product istypically coated with mineral granules to provide durability, reflectheat and solar radiation, and to protect the bituminous binder fromenvironmental degradation. The solar reflective roofing granules of thepresent invention can be mixed with conventional roofing granules, andthe granule mixture can be embedded in the surface of such bituminousroofing products using conventional methods. Alternatively, the solarreflective roofing granules of the present invention can be substitutedfor conventional roofing granules in manufacture of bituminous roofingproducts.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Roofing granules are then distributed over selected portions ofthe top of the sheet, and the bituminous material serves as an adhesiveto bind the roofing granules to the sheet when the bituminous materialhas cooled. The sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation and aesthetic effect, additional bituminous adhesive can beapplied in strategic locations and covered with release paper to providefor securing successive courses of shingles during roof installation,and the finished shingles can be packaged. More complex methods ofshingle construction can also be employed, such as building up multiplelayers of sheet in selected portions of the shingle to provide anenhanced visual appearance, or to simulate other types of roofingproducts. Alternatively, the sheet can be formed into membranes or rollgoods for commercial or industrial roofing applications.

The bituminous material used in manufacturing roofing products accordingto the present invention is derived from a petroleum-processingby-product such as pitch, “straight-run” bitumen, or “blown” bitumen.The bituminous material can be modified with extender materials such asoils, petroleum extracts, and/or petroleum residues. The bituminousmaterial can include various modifying ingredients such as polymericmaterials, such as SBS (styrene-butadiene-styrene) block copolymers,resins, flame-retardant materials, oils, stabilizing materials,anti-static compounds, and the like. Preferably, the total amount byweight of such modifying ingredients is not more than about 15 percentof the total weight of the bituminous material. The bituminous materialcan also include amorphous polyolefins, up to about 25 percent byweight. Examples of suitable amorphous polyolefins include atacticpolypropylene, ethylene-propylene rubber, etc. Preferably, the amorphouspolyolefins employed have a softening point of from about 130 degrees C.to about 160 degrees C. The bituminous composition can also include asuitable filler, such as calcium carbonate, talc, carbon black, stonedust, or fly ash, preferably in an amount from about 10 percent to 70percent by weight of the bituminous composite material.

Example

Particles with high solar reflectance are prepared by agglomerating theappropriate materials in an Eirich RV02 mixer using the followingprocedure. A quantity of the kaolin material (Calcined Plastic Fireclayby Christy Minerals) and a drilling starch binder were disposed into anEirich mixer and dry mixed for 30 seconds. De-ionized water was thenadded over a 30 second period as the mixer continued to rotate andspheres of base material were formed. After approximately four minutesof mixing the base material, binder and water, the TiO₂ pigment material(CR-826, available from Tronox, Okla. City, Okla.) was slowly added over3 to 5 minutes to the mass of rotating spherically shaped bases bysprinkling (also known as “dusting in”) the layer material on top of thebases as they were moving in the mixer until uniform distribution of theTiO₂ pigment on particle surface was observed. Samples contain variousamounts of kaolin material and TiO₂ pigments which total a constant 15lbs. The formed particles were then spread on a tray and dried in aforced air oven and were then fired to sinter in a static kiln atvarious temperatures to form solar reflective particles. The amount ofTiO₂ pigments and the firing temperatures are listed in Table 1, alongwith the color reading, solar reflectance (ASTM C-1549 method), and theUV opacity (ARMA Granule Test Manual Test Method #9) of the resultantparticles. In Table 2, the particle size data of the resultant particlesare listed. As one can see, the particles have high solar reflectancewith suitable sizes for roofing applications.

TABLE 1 Firing TiO2 Temp. Color Reading Solar % UV wt % ° C. L* a* b*Reflectance Opacity 0 900 82.38 5.55 9.18 0.697 NA 0 1200 88.05 1.477.21 0.746 93 0 1450 87.91 0.82 11.49 0.78 94.9 20 900 84.86 2.14 9.620.725 NA 20 1200 81.71 2.49 18.14 0.712 92 20 1450 70.67 8.04 27.520.623 97 30 900 86.57 1.74 9.25 0.749 NA 30 1200 82 2.05 17.13 0.719 9930 1450 68.95 8.42 27.08 0.625 99 40 900 87.63 0.74 7.1 0.749 NA 40 120081.51 1.38 15.07 0.708 100 40 1450 68.25 8.21 26.08 0.628 100

TABLE 2 Firing TiO2 Temp. Sieve Analysis, wt % retaining on US mesh sizewt % ° C. #8 #12 #16 #20 #30 #40 Pan 0 900 5.54 17.52 48.66 23.43 3.030.27 1.41 0 1200 6.42 16.08 46.62 25.03 4.24 0.43 1.19 0 1450 2.39 8.1537.54 39.97 9.55 1.89 0.05 20 900 14.59 25.2 34.31 18.49 5.02 1.27 1.1220 1200 11.97 20.23 33.78 24.52 7.32 1.8 0.38 20 1450 7.87 15.46 31.1329.18 11.44 3.89 1.03 30 900 2.45 15.4 46.42 30.74 4.52 0.29 0.18 301200 1.61 8.19 35.57 41.67 11.28 1.53 0.15 30 1450 1.22 7.26 30.91 44.3513.83 2.3 0.13 40 900 1.74 21.38 46.6 25.875 4.04 0.34 0.1 40 1200 0.6411.95 44.28 36.99 5.54 0.13 0 40 1450 0.21 7.85 36.85 40.9 11.8 2.140.25

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

1-14. (canceled)
 15. Solar reflective roofing granules, each comprising(a) a granule body comprising inert mineral particles or ceramicparticles bound by an inorganic binder, the granule body having anexterior surface; and (b) solar reflective particles, the solarreflective particles being adhered to the granule body only at orproximate to the exterior surface of the granule.
 16. Solar reflectiveroofing granules according to claim 15 wherein the solar reflectiveparticles are mechanically adhered to the exterior surface of thegranule bodies.
 17. Solar reflective roofing granules according to claim15 wherein the solar reflective particles are selected from the groupconsisting of titanium dioxides, metal pigments, titanates, and metalreflective pigments.
 18. Solar reflective roofing granules according toclaim 15 wherein the granule body comprises inert mineral particles. 19.Solar reflective roofing granules according to claim 18 wherein theinert mineral particles have an average particle size from about 0.1micrometers to about 40 micrometers.
 20. Solar reflective roofinggranules according to claim 15 wherein the granule body comprisesceramic particles.
 21. Solar reflective roofing granules according toclaim 15 wherein the binder is selected from the group consisting ofsilicate, silica, phosphate, titanate, zirconate, and aluminate binders,and mixtures thereof.
 22. Solar reflective roofing granules according toclaim 21 wherein the binder further comprises aluminosilicate or kaolinclay.
 23. Solar reflective roofing granules according to claim 15,wherein each granule further comprises a coloring pigment.
 24. Solarreflective roofing granules according to claim 15 having a solarreflectance of at least about 60%.
 25. A roofing product comprisingsolar reflective roofing granules according to claim
 15. 26. The roofingproduct according to claim 25, wherein the roofing product is in theform of a shingle comprising a bituminous substrate having the solarreflective roofing granules adhered to a surface thereof.
 27. Solarreflective roofing granules, each granule comprising a granule bodycomprising ceramic particles and solar reflective particleshomogeneously dispersed with one another and bound by an inorganicbinder, the granule body having an exterior surface, a plurality of thesolar reflective particles being located at or proximate to the exteriorsurface of the granule.
 28. Solar reflective roofing granules accordingto claim 27 wherein the solar reflective particles are selected from thegroup consisting of titanium dioxides, metal pigments, titanates, andmetal reflective pigments.
 29. Solar reflective roofing granulesaccording to claim 27 wherein the binder is selected from the groupconsisting of silicate, silica, phosphate, titanate, zirconate, andaluminate binders, and mixtures thereof.
 30. Solar reflective roofinggranules according to claim 29 wherein the binder further comprises aninorganic material selected from the group consisting of aluminosilicateand kaolin clay.
 31. Solar reflective roofing granules according toclaim 27 having a solar reflectance of at least about 60%.
 32. Solarreflective roofing granules according to claim 27, wherein each granulebody further comprises a coloring pigment bound together with theceramic particles and the solar reflective particles by the binder. 33.A roofing product comprising solar reflective roofing granules accordingto claim
 27. 34. The roofing product according to claim 33, wherein theroofing product is in the form of a shingle comprising a bituminoussubstrate having the solar reflective roofing granules adhered to asurface thereof.